Integrated circuits may be formed using various photolithographic techniques. Such techniques typically include use of a Chemical Mechanical Polishing (CMP) process. The CMP process is typically used to grind down and smooth the surface of a semiconductor substrate. In some cases, the CMP process is used to remove some or all of previously formed layer(s) that are no longer needed. For example, trenches may be formed into a semiconductor substrate. Various other layers of material may be deposited within the trenches. To simplify the deposition process, these layers are deposited on the entire semiconductor substrate, including the trench areas and non-trench areas. To remove the deposited layers from the non-trench areas, the CMP process may be applied to grind away the deposited layers.
The CMP process uses a slurry that includes a chemical solution with a specific viscosity that will hold very small particles. The particles are made of a hard material such as silica (SiO2) or alumina (Al2O3). These particles help grind away and smooth the surface of the substrate. These particles should be within a specific size range. Particles that are too large can cause unwanted scratches on the surface of the semiconductor substrate. Particles that are too small will not effectively grind the surface of the substrate. Thus, the CMP slurry is typically put through a filter to remove larger pieces. It is desirable, however, to have a solution with fewer large particles that have to be filtered out.